Electric motor speed control mechanism



Oct. 4, 1955 R. H. TULL ELECTRIC MOTOR SPEED CONTROL MECHANISM FiledNov. 15, 1951 2 Sheets-Sheet l INVENTOR Robert H. Tull WITNESSES:

ATTORNEY Oct. 4, 1955 R. H. TULL 2,719,945

ELECTRIC MOTOR SPEED CONTROL MECHANISM Filed NOV. 15, 1951 2Sheets-Sheet 2 WITNESSES: INVENTOR UW. N Q Robert H. Tull BY Q W ATTO RNEY ELECTRIC MOTOR SPEED CONTROL MECHANISM Robert H. Tull, Wilbraham,Mass., assignor to Westinghouse Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Application November 13, 1951, SerialNo. 256,060

4 Claims. (Cl. 318-325) My invention relates to a control mechanism thatincludes a regulating mechanism and a manually operated knob or the likemovable to several different positions to adjust the regulatingmechanism to different settings and movable to still another position,designated an off position, in which operation of the controlled deviceis terminated. It is particularly applicable, for example, to a speedcontrol mechanism'for a food mixer motor.

The object of the invention is to provide improved means for effectingadjustment between the manually actuated member and the regulatingmechanism.

In the preferred embodiment of my invention, I provide a manuallyoperable knob which comprises an outer part and an inner part telescopedwithin the outer part. The outer part and a stationary member haveindicia-designating an off position and a plurality of operatingpositions, and the outer part has a cam which is adapted to open thecircuit when theknob is in the off position. The inner part has a camsurface for adjusting the setting of the regulating mechanism. The innerand outer parts of the knob have interlocking portions or teeth wherebythe inner part can be inserted in the outer part in any one of severalrelative positions, said interlocking portions preventing relativerotation of the inner and outer parts from the relative position inwhich they are assembled. Y

Also, in the preferredembodiment, the inner part is mounted so that itis operable to adjust the setting of the regulating mechanism and thecontrolled device is adapted to be operated even though the outer partis removed. Thus, the inner part may be rotated until the condition,such as speed, corresponding to one of the indicia is obtained. Theouter part is turned to the rotative position designated by suchindicium and telescoped over the inner part. The inner and outer partsof the knob are thus assembled in proper relative position to providethe setting of the regulating mechanism called for by the in dicium atwhich the knob is positioned.

The above and other objects are effected by my invention as will beapparent from the following descrip tion and claims taken in connectionwith the accompanying drawings, forming a part of this application, inwhich:

Fig. 1 is a longitudinal vertical section of an electric motor used in afood mixer and provided with a speed control mechanism in accordancewith my invention;

Fig. 2 is an exploded view showing the parts which carry the two partsof the knob spaced from each other;

Fig. 3 is a bottom plan view of the control knob; and

Fig. 4 is a top plan view of the control knob, with parts broken away.

Referring to the drawings in detail, I show an electric motor which isused in a food mixer and which is en closed within a casing having alower part or base 11 and an upper part or cover 12. The base 11 may beprovided with an extension 13 for pivotally connecting the motor to thepedestal of the mixer base. The motor parts are mounted on the lowerpart 11 and the motor is adapted to operate while the cover 12 isremoved. The stator '14 nited States Patent "ice and the bearing 15 areheld against their seats formed in the base 11 by a spring structure 17which is fastened to the base at 18, as more fully disclosed in RitterPatent No. 2,469,932. A reduction gear casing 19 is formed partly by amember integral with the base 11 and partly by a gear case cover 21,which also serves to retain the shaft bearing 16 against its seat. Apost 22 is fastened to the gear case cover 21 in permanent fixedrelation and extends upwardly through an opening in the cover 12.

A speed governor 23 is also mounted on the base 11 and includescontact-carrying arms 24 and 25, which are self-biased forwardly, or tothe right as shown in Fig. 1, and which carry cooperating contacts 26and 27 adapted to engage and disengage as the arms move toward and awayfrom each other. The contacts are connected in the motor circuit in aknown manner so that when they are open they interrupt the current tothe motor either completely or partially to reduce the speed of themotor. The governor further includes centrifugal Weights 28 carried bythe connected ends of two oppositely bowed spring strips 29 and 31. Thespring strip 29 is connected, at the center of rotation, to the motorshaft, and the spring member 31 carries an insulating button 32 disposedat the axis of rotation and adapted to contact and to actuate the arm24.

A handle 32 is connected at its rear end to the cover 12. The front endis connected to the upper end of the post 22 by means of a screw 33which extends through a thimble 34 fixed to the handle and which isscrewthreaded into the upper end of the post 22.

The speed adjusting knob, to which this invention particularly relates,is shown at 35 and comprises an outer part 36 and an inner part 37,assembled in telescoped relation as shown in Fig. 1.

The inner part 37 is mounted for rotation about the post 22, and has acentral circular opening through which the post 22 extends. The innerpart has a spiral groove 38 formed in the lower face thereof foradjusting the speed setting of the speed governor 23. A slide bar 39 isprovided to transmit motion to the governor, and it is provided with apin or projection 40 which is received in the groove 38 and with abutton 41 which bears against the contact arm 25. The bar 39 is providedwith a slot 42 through which the post 22 extends, and it extends throughan opening in a bracket 43, whereby the bar is mounted and guided forlongitudinal sliding movement. A tension spring 44 may be provided tocause the pin 40 always to bear against the radially inner side of thegroove 38, thereby avoiding change in speed setting by reason of lostmotion of the pin in the groove.

The outer part 36 of the knob is of inverted cup shape and is rotatablymounted on the thimble 34 carried by the handle. The thimble extendsthrough a circular opening in the top Wall of the outer part 36, whichis retained on the thimble by a ring 45. The outer part 36 includes anupper grip portion 46 and a lower flange portion 47 which bears variousindicia for the various positions. A projection or pointer 4-8 isprovided on the cover'12, and the indicium adjacent the projection 48designates the position of the knob. On the bottom, the outer part isformed with a cam surface that actuates a line switch 49 including aspring arm 51 which carries the movable contact. The switch 49, whenopen, completely interiupts the supply of electric current to the motorregardless of the contacts 26 and 27. The cam surface, as shown moreparticularly in Fig; 2, includes a portion 52 of uniform height and arecess or lower portion 53 connected by an inclined portion 54. Therecess 53 of the cam surface and the off indicia of the outer knob part36 are in fixed relation such that when the knob is in the off positionin which the off indicia is at the projection 48, the recess 53 is inalignment with the switch arm 51 and permits the same to be in openposition. When the knob is rotated to an operating position, theinclined portion 54 moves the lever 51 downwardly to close the lineswitch and the lower uniform surface 52 holds the line switch closed inall operating positions.

In order to hold the switch arm 51 down to close the line switch 49While the outer knob part 36 is removed, there is provided a flexiblearm 55 which is pivotally or rotatably mounted on the post 22 betweenthe slide bar 39 and the gear case cover 21. When the cover 12 isassembled, the arm 55 is swung to the left as shown in Fig. l.

The outer knob part 36 is further provided with a downwardly extendingprojection 56 which is adapted to abut the bar 39 to limit the rotationof the knob to a value slightly less than 360 degrees, and thereby toprevent continuous rotation of the knob. The projection 56 is alsouseful in swinging the arm 55 to a position under the bar 39 after thecover is assembled.

Referring again to the telescoping relation of the knob parts as shownin Fig. 1, the inner part 37 has a convex cylindrical peripheral surface57 (Fig. 3) which fits a concave cylindrical surface 53 in the outerpart 36. In order to hold the inner and outer parts against relativerotation from the desired relative position, the outer part is providedwith a plurality of teeth 59 which project radially inwardly from theconcave surface 58, and the inner part 37 is formed with cooperatinginterlocking teeth 61 which are adapted to interlock or intcrmesh withthe teeth 59. The spaces or recesses between adjacent teeth 59 areadapted to receive the teeth 61 of the outer part. The teeth 61 and therecesses therebetween are disposed within the cylinder defined by thecylindrical surface 57. Since the teeth 59 project inwardly of thecylinder defined by the surfaces 57 and 53, the inner and outer partscan be assembled only in a relative position in which the teeth 59 arewithin the angular extent of the teeth 61, so that they can be receivedWithin the recesses between the teeth 61. The number of teeth 61 is substantially greater than the number of teeth 59, so that a limited rangeof relative angular adjustment is thereby provided.

Operation Operation of the speed governor will first be considered.

Assume the slide bar 39 to be in a given position and the motor to beconnected to a supply of electric current. As the motor increases inspeed, the weights 28 draw the two spring arms 29 and 31 toward eachother, and the arms 24 and 25 move to the right, as seen in Fig. 1, asthey follow the button 32. As the arm 25 engages the button 41, it isheld stationary, and upon further movement of the arm 24 accompanyingcontinued increase in speed of the motor, the arm 24 moves its contact26 out of engagement with the contact 27 to decrease the currentsupplied to the motor. The speed then decreases and the spring forces ofthe arms 29 and 31 cause them to separate. The button 32 then moves thearm 24 toward the arm 25 to re-engage the contacts, thereby energizingthe motor. This cycle of energizing and deenergizing the motor iscontinually repeated so as to restrict the speed of the motor to a smallrange extending slightly above and slightly below a selected speed atwhich the contacts open and close.

As the slide bar 39 is moved to the right, away from the arm 25, thegovernor is adjusted to a higher speed setting, since a higher speedwill be required to move the contact arm 24 out of engagement with thearm 25. Conversely, upon moving the slide bar 39 to the left against thearm 25, a lower speed setting is obtained, since a lower speed isrequired to bring the arm 24 into engagement with the arm 25. Toincrease the speed of the motor during use of the food mixer, the knob35 is turned clockwise (counterclockwise as seen in Fig. 3). Upon suchrotation of the knob, the slide bar 39 is drawn forwardly or to theright by engagement of the projection 40 in the groove 38, to increasethe speed setting as just described. Upon rotation of the knob incounterclockwise direction (clockwise as seen in Fig. 3), the slide bar39 is moved to the left by such engagement of the pin or projection 40in the groove 38, thereby lowering the speed setting. Continued rotationof the knob to the off position brings the recess 53 into alignment withthe arm 51, which is self-biased upwardly, and thereby opens the switch49 to completely deenergize and terminate operation of the motor. Toinitiate operation of the motor, the knob is turned from the offposition to one of the operating positions and as the inclined camsurface 54 passes over the lever 51, it depresses the same to close theswitch 49, so that the motor is energized under control of the speedgovernor.

To provide adjustment between the speed governor and the speed adjustingknob, the cover 12 is removed and the arm 55 is swung into alignmentwith the arm 51 to depress the same to closed position. Suitableconnection to a source of electric current being made as by theconventional cord and plug, the motor is now energized and operating. Atachometer is applied to the shaft and the inner knob part 37 isadjusted until a preselected speed, corresponding to one of the indiciaand arbitrarily selected for test purposes, is attained. The arm 55 isthen rotated to open the switch 49, while the inner part 37 is retainedin the position at which the preselected speed was attained. The outerknob part 36 is rotated to bring the indicia which calls for thepreselected speed opposite the projection 48, and the cover is thenassembled to the base 11 and secured thereto by any suitable means (notshown), and the screw 33 is inserted to securely attach the handle 32 tothe post 22. During such assembly, the group of teeth 59 of the outerknob part enter recesses between adjacent teeth 61, thereby providing aninterlocking relation between the outer and inner parts that preventstheir relative rotation. The inner and outer parts are now assembled andheld in their proper relative position so that as the knob is rotated tothe different operating positions, the desired speed of the motor isobtained. While only the preselected speed is individually adjusted, thevariation in speed effected by rotation of the knob is adquatelycontrolled by the design of the cam groove 38, so that substantially thecorrect or desired speed is obtained for each operating position of theknob.

While I have shown my invention in but one form, it will be obvious tothose skilled in the art that it is not so limited, but is susceptibleof various changes and modifications without departing from the spiritthereof.

What I claim is:

1. An electric motor comprising a casing having a lower section and anupper section or cover, a post mounted on structure supported by saidlower section, said post extending upwardly through said cover, a handleattached at one end to said cover and at its other end to the upper endof said post, a manually operable control knob, including an upper partand a lower part, mounted for rotation about said post, said upper andlower parts of the knob having interlocking portions which permit theparts to be assembled in any one of several relative positions butinterlock the parts against relative rotation, said knob parts beingretained in assembled interlocked relation by and between said other endof the handle and structure supported by the lower casing section, eachof said knob parts having a cam surface, and a line switch and a speedgovernor within the casing, said line switch being operated by the camsurface of one of said parts and the cam surface on the other of saidparts adjusting the speed setting of the speed governor when the knob isrotated.

2. An electric motor comprising a casing having a lower section and anupper section or cover, a post mounted on structure supported by saidlower section, said post extending upwardly through said cover, a handleattached at one end to said cover and at its other end to the upper endof said post, a manually operable control knob mounted concentricallywith said post and comprising a lower part rotatable about said post andan upper part rotatably supported by said other end of the handle, saidupper and lower parts having interlocking portions permitting the partsto be assembled in any one of several relative positions but preventingrelative rotation between the parts, each of said parts having a camsurface, a line switch and a speed governor supported on the lowercasing section, said line switch being operated by the cam surface ofsaid upper part and said cam surface on the lower part adjusting thespeed setting of the speed governor when the knob is rotated, wherebythere is provided a construction wherein said upper knob is assembledwith said lower knob part in interlocking relation when the upper andlower sections of the casing are assembled as a unit.

3. The combination with an electric motor, of a speed control mechanismtherefor including a rotatable manually operable knob which comprises aninner and an outer part, said parts being axially movable into and outof telescoping relation and having interlocking portions which permitassembly of such parts in any one of several relative positionsangularly displaced from each other but which prevent relative rotationof said parts when they are in telescoped relation, each of said partshaving a cam surface, means for mounting said inner part for rotationindependently of the outer part, a speed governor operable to controlthe supply of electrical energy to the motor in response to the speedthereof, means including a cam follower actuated by the cam surface onsaid inner part for adjusting the speed setting of said speed governor,a line switch adapted to open the circuit to the motor, said line switchbeing adapted to be actuated to closed position by the cam surface onsaid outer knob part, and other means normally disposed out ofengagement with said line switch but movable into engagement therewithto hold the same in closed position when said outer knob part isremoved, whereby said inner knob part may be adjusted to effect apredetermined speed setting of the governor while said outer knob partis removed to facilitate assembly of said knob parts in proper angularrelation.

4. An electric motor comprising a casing having a lower part and anupper part or cover, a post mounted on the lower casing part andextending upwardly through said cover, a handle attached at one end tosaid cover and at its other end to the upper end of said post, amanually operable control knob mounted concentrically with said post andcomprising an inner part mounted on said post and an outer part mountedon said handle, said inner and outer patrs having interlocking portionspermitting insertion of the inner part within the outer part in any oneof several relative positions but preventing relative rotation when itis inserted, each of said parts having a cam surface, a line switchmounted on the lower casing part and operated by the cam surface of saidouter knob part, a speed governor mounted on the lower casing part, anda connecting mechanism operated by the cam on said inner knob part foradjusting the speed setting of said speed governor.

References Cited in the file of this patent UNITED STATES PATENTS2,262,306 Thompson Nov. 11, 1941 2,557,765 Robertson June 19, 19512,623,961 Holstein Dec. 30, 1952

